Rajasthan Technical University 2009-3rd Sem B.E : Electrical Engineering (- ) Electrical Measurment - Question Paper
Rajasthan tech. University(RTU)
B.Tech III sem. Main exam
January 2009
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Roll No.: 0 *1 F ~~T _ Total Printed Pa9l
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B. Tech. (Sem. Ill) (Main/Back) Examination, January (3EE5) Electrical Measurements
(Electrical Engineering)
3E1485
Time: 3 Hours] [Total faafks +60'*'
[Min. Passing Marks : 24
Attempt five questions in all. Schematic diagrams must be shown wherever necessary. Any data you feel missing may suitably be assumed and stated clearly.
Use of following supporting material is permitted during examination. (Mentioned in form No. 205)
1.__ Nil 2. N
1 Describe with neat diagram construction and working principle of electro dynamometer type wattmeter. Derive torque equation and discuss various errors in this type of wattmeter.
8+8
1 Explain giving a neat sketch the construction and principle of operation of a single phase induction type of energymeter. Derive its torque equation. Also explain phantom loading method of testing single-phase induction type energy meter.
8+4+4
2 (a) Explain how power can be measured in a three phase
circuit with the help of two wattmeters. Illustrate with
the help of a piiasor diagiaia for a balanced star load.
3E1485J IHBinill 1
*3E1<85*
[Contd...
(b) Two wattmeters connected to measure th&'Duf to a balanced three phase circuit indicate 2000 WW
j r -; {
JIV
respectively. Find the powier factor of circuit :
(i) When both the readings are positive.
(ii) When the latter reading is obtained after reversing the connections to the current coil of first instrument.
4+4
(a) Draw the equivalent circuit and the phasor diagram of a current transformer. Derive the expression for its ratio and phase angle errors.
3+3+3+3
(b) Explain why the secondary of the current transformer should not be opened when primary is energized.
4
(a) Explain the term "standardization" of a potentiometer. Draw the circuit diagram of a 'Crompton's potentiometer and explain its working.
, 2+6
(b) Describe with the help of suitable diagrams, how a D.C. potentiometer can be used for :
(i) Calibration of a wattmeter.
(ii) Determination of an unknown resistance.
4+4
(a) Describe the construction and working of a co-ordinate type A.C. pocenuometei. now is re staiidaxdized. l >>
an unknown voltage can be measured with it.
6+2+2
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(b) A co-ordinate type potentiometer is used for determin of impedance of a coil and the results obtained are
Voltage across a 1.0 ohm resistor in geries with the +0.238 V on in-phase dial and -0.085 V on a quadrature dial.
Voltage across a 10:1 potential divider used with the coil: +0.3375 V on in-phase dial and +0.232 V on quadrature dial.
Calculate the resistance and reactance of the coil.
3+3
Why are the low resistance constructed to be of four terminal type ?
4 (a) (b)
4 (a) (b)
4
Draw the circuit of a Kelvin's double bridge used for measurement of low resistance. Derive the condition for balance. Explain how the resistance of connecting leads is
r
eliminated.
Mention the different problems associated with measurement of high resistance.
Explain price's guard-wire method for the measurement of insulation resistance of a cable.
10
5 (a) Describe the sources and the null detectors that are used for A.C. bridges.
4
(b) Derive the equations of balance for an Anderson's bridge. Draw the phasor diagram for conditions under balance.
TWcspiicjc fj/o d?e,dvjf>Ttf)sj'e)s of the bridcfe.
6+3+3
OR
[Contd..
O'
(a) Explain the function and working of Wagnartl: device.
** /-k1
(b>* The four arms of Maxwell's inductance capacitance brmgeT at balance are :
*
Arm ab : Unknown inductance of and inherefi?listance of %
Arm be : Non-inductive resistance of 1000 ohm.
Arm cd : A capacitor of 0.5 yF in parallel with a resistance of 1000 ohm.
Arm da :A non-inductive resitance of 1000 ohm. Determine the value of and L1.
4+4
[ 4400 ]
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| Earning: Approval pending. |
